Magnetic core structure



Oct. 13, 1 c. E. BURKHARDT ETAL 3,153,215

MAGNETIC CORE STRUCTURE Original Filed Oct. 15, 1958 4 Sheets-Sheet 1 Fig. 2

54A 545 54c 540 54E 54F I mvsmoas 98 Charles E. Burkhordi a Flg. 4 Belvin 5. Ellis cau i f. W; ALL

ATTORNEY Oct. 13, 1964 c. E. BURKHARDT ETAL 3,153,215

MAGNETIC CORE STRUCTURE Original Filed 0015. 15, 1958 4 Sheets-Sheet 2 2 4 0 m w 4 v 7 2 ql. TB 8 H l 44 B 4 2 w n w I. 4 z m m a a m Z 4 4,1 3. 4 w 5 v fl wfi $.03 4.4.. mTbH 24680 MIBA llll 2 .m M F p 5 5 5 2 6 3|. 4 p m K 4 2 n. w 2 H r5 2 5B 2 M 4 M 4 Ru. H m g I F Fig. I0

Fig. u

.Fig. 9

Oct. 13, 1964 c. E. BURKHARDT ETAL 3,153,215

MAGNETIC coma STRUCTURE Original Filed Oct. 15, 1958 4 Sheets-Sheet 5 224.] Fig. 9A.

Oct. 13, 1964 c. E. BURKHARDT ETAL 3,153,215

MAGNETIC CORE STRUCTURE Original Filed Oct. 15. 1958 4 Sheets-Sheet 4 4 4 W, w w W Fig. 2|

United States Patent 22 (Ilaims. (Cl- 336-217) This invention relates to magnetic core structures for use in electrical inductive apparatus, such as transformers. This applicationis a division of our application Serial No. 767,422, filed October 15, 1958, nowabandoned, and assigned to the same assignee as the present applica tion. i

in certain types of electrical inductive apparatus, such as transformers, a magnetic core structure is provided which includes a plurality of stacked layers of laminations formed from a magnetic strip material, preferably a material having a preferred direction of orientation parallel to the longitudinal dimension of said material.

In order to obt in more efficient joints between the laminations, a conventional core of this type often employs combination butt and lap joints adjacent to the corners of the core structure in which the adjoining edges of the laminations are cut at an angle to the direction of the strip material in order to obtain a higher permeability of the core structure and lower losses in the core structure. An example of a conventional core of the type described is shown in US. Patent 2,300,964, issued November 3, 1942, on an application of H. V. Putman and assigned to the assignee of the present application. One disadvantage of a conventional core of the type described is that great care must be exercised in the assembly and the stacking of the laminations in order to obtain a satisfactory magnetic performance. to the lower limits of the exciting current and the associated losses which can ordinarily be obtained in a conventional magnetic core. It is therefore desirable to provide an improved magnetic core structure which requires a lower exciting current and has reduced losses associated with the core compared to a conventional magnetic core of the same general type. an improved core also more readily lend itself to convenient assembly with an associatedelectrical winding than a conventional magnetic core. I

It is an object of this invention to provide a new and improved magnetic core for electrical inductive apparatus, such as transformers.

Another'object of this invention is to provide a new and improved magnetic core of the stacked type.

A further object of this invention is to provide a new and improved magnetic core forelectrical inductive apparatus including a plurality of stacked layers of laminations formed from magnetic strip material having a preferred direction of orientation lengthwise of said strip material. Other objects of the invention will in part be obvious and will in part appear hereinafter.

For a fuller understanding of the nature and'ohjec A second disadvantage of such core relates;

In addition, it is desirable that of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawings in which:

FIGURE 1 is a perspective view of a magnetic core illustratingafirst embodiment of the invention. I

FIG. 2 is a partial view, in side elevation, of the magnetic core shown in FIG. 1.

FIG. 3illustrates parts of the magnetic core structure shown in FIG. 1.

FIG. 4 is a perspective view of a magnetic core illustrating a second embodiment of the invention.

layers 42 is preferably 3&53215 Patented Oct. 13., 1964 magnetic core shown in FIG. 5 taken along the line VII- VII.

FIG. 8 illustrates shown inFlG. 5.

FIG. 9 shows a partial View, in front elevation, of a magnetic core illustrating a fourthernbodiment of the invention.

FIGhQA illustrates a three phase magnetic core of the parts of themagnetic core structure core from type which utilizes the embodiment of the invention shown in FIG. 9. a

FIG. 10 illustrates parts of the magnetic core structure shown in FIG. 9. 7

FIG. 11 is a partial view, in side elevation, netic core shown in FIG. 9.

FIG. 12 is an enlarged partial View, in section, of the magnetic core shown in FIG. 9, taken along the line XII- XII.

FIG. 13 is an enlarged partialview, in section, illustrating an alternate arrangement of the laminations in a magnetic core of the type shown in FIG. 9. i

FIG. 14 is a top plan view of a core and coil assembly, with the windings shown in phantom, illustrating a fifth embodiment of the invention.

FIG. 15 is an enlarged partial view, in section, of the magnetic core shown in FIG. 14, taken along the line XV-XV.

FIG. 16 is an enlarged partial view, in section, illustrating an alternate arrangement of the laminations in a mag netic core of the type shown in FIG. 14.

FIG. 17 is a partial plan view of a magnetic core, having a construction similar to the magnetic core shown in FIG. 14.

' FIG. 18 is a partial plan view of another magnetic core, having a construction similar to the magnetic core construction shown in FIG. 14. t i

of the mag- FlG. 19 is a partial view, in side elevation, of the mag netic core shownin FIG.18.

FIG. 20 illustrates parts of the magnetic core'structure shown in FIGS. 5A, 9A, and 14; and

FIG. 21 is an enlarged partial view, in section, illustrating an alternate arrangement of the laminations in a magnetic core of the type shown in FIG. 14.

Referring now to the drawing and FIGURES 1 and 2 in particular, there is illustrated generally a magnetic core 30 of the stacked type. The magnetic core Stl'comprises one or more groups'of layers of laminations. Each group includes a plurality of stacked sembled to form a substantially rectangular core, having in this particular case two substantially rectangular windows.

Referring to FIG'Z, there are illustrated two groups 49 and 69, each including a plurality of layers 42, each layer of laminations including at least first and" second yoke laminations and first and second leg laminations. Referring to FIG. 1, each layer 42 includes the that and second yoke laminations 5S and 78, respectively, and the first and second outer leg larninations 52 and 56, respectively, and a center leg lamination 5 5. It is to be understood that the center leg lamination 54 may not be included in particular apparatus having a magnetic core similar to that disclosed in FIGrl.

Each ofthe leg laminations 52, 54

and 56 and each of the yoke laminations 58 and '78 included in each of the t formed from a magnetic strip material having a preferred direction of orientation lengthlayers of laminations as-fl wise of said material or parallel to the sides or to the longitudinal dimension of said material. The ends of the leg laminations S2 and 56 and the ends of the yoke laminations 58 and 73 are cut diagonally with respect to the longitudinal dimension of the magnetic strip material from which said laminations are formed, preferably at an angle of substantially The ends of the center leg laminations 54 are cut to be generally V-shaped and the yoke laminations 58 and 78 each includes a matching generally V-shaped recess to accommodate the cut ends of the associated center leg laminations 54.

The leg laminations 52, 54 and 56 and the yoke laminations 58 and 78 included in each of the layers 42 are assembled around two substantially rectangular windows, as shown in FIG. '1, with the adjoining cut ends of said laminations in each layer substantially aligned to form diagonal joints between the respective ends of the laminations as indicated at 53, 55, 63, 59, 57 and 69. The latter joints are arranged so that the direction of travel of the magnetic flux in the magnetic core 39 substantially coincides with the preferred direction of orientation of the magnetic strip material from which said laminations are formed.

Referring to FIG. 2, the layers 42 which make up each of the groups 4t) and 60 are stacked with the ends of the laminations which make up each of the respective layers 42 arranged in stepped relation with respect to the ends of the corresponding laminations in the adjacent layers 42 to overlap the joints between the ends of the laminations in the adjacent layers. The extent or distance of the overlapping should preferably be at least six times the thickness of each of the laminations included in the core 30. It is to be noted that the layers 42 included in each of the groups of layers 40 and 6% may be disposed in a recurring or repeating pattern as shown in FIG. 2, with the direction of the slope of the lapped joints being the same in each of the groups included in the core St) or with the slopes of the joints in alternate groups being in opposite directions.

Referring to FIGS. 1 and 3, several methods may be employed to obtain the stepped relation between the ends of the corresponding laminations in the successive layers 42 included in each of the groups 4% and shown in FIG. 2. One method includes the use of the positioning holes 72, 76 and 74 associated with the first and second outer leg laminations 52 and 56 and the center leg lamination 54 as shown in FIG. 1. The positioning holes 72, 74 and '76 are made in a stepped pattern in successive layers 42. The positioning holes 72, 74 and 76 are in-- dexed or staggered in successive layers of laminations so that said holes are spaced apart in relative position on successive corresponding laminations by a small incremental distance. The latter incremental distance between the ends of the successive corresponding laminations in the respective layers 42 determines the extent of the overlapping of the cut ends of the laminations when assembled in the final core 38.

Referring to FIG. 3, there is shown in detail the manner in which the positioning holes 74 are staggered or offset in the center leg laminations 54. The positioning holes 74A to 74F in six successive center leg laminations 54A to 54F, respectively, are illustrated. The number of positioning hole positions in the leg laminations 52, and 56 determines the number of steps in the lap joints of each of the groups 40 and 6% shown in FIG. 2. In the assembly of the laminations included in the magnetic core 36 the positioning holes '72, 74 and 76 are substantially aligned, as shown in FIG. 2 in order to arrange the cut ends of the laminations in successive layers of the core 3% in stepped relation.

A second alternative method of arranging the lamina tions of the core 30 in stepped relation in successive layers is to provide positioning recesses 82, 86 and 84- on the first and second outer leg laminations 52 and 56 and the center leg laminations 54-, respectively, in similar manner to the it positioning holes '72, 76 and 7d. The indexing of the positioning recesses on the center leg laminations 54A to 54F is shown in FIG. 3 and includes the positioning recesses 84A to 84?, respectively, on said center leg laminations.

It is to be noted that the groups 4-43 and 6%) shown in FIG. 2 each includes a series of lap joints between the laminations included in each of the layers 42 arranged in stepped relation. The ratio of the overlapping distance to the thickness of each lamination may be varied in a particular application. It has been found that a magnetic core of the stacked type as shown in FIGS. 1 and 2, including one or more groups of layers of laminations with the joints between the laminations arranged to form a stepped-lap joint in each group, has a lower exciting current and associated losses than a conventional magnetic core of the same type. The stepped-lap joint in each group of layers of laminations in the magnetic core 50 extends through a substantial portion of the overall core thickness, preferably through at least six layers of the laminations of said core, and as previously stated, the ends of the corresponding laminations included in each of the layers 42 over-lap one another in successive layers by a substantial amount, preferably by a distance equal to at least six times the thickness of each of the laminations.

Although the core 34) shown in FIGS. 1 and 2 is illustrated as being of the three phase, core-form type, on whose winding leg portions electrical windings (not shown) may be disposed, it is to be understood that a similar construction may be employed in apparatus requiring a single phase magnetic core having a single window and either one or two winding leg portions or in a three-phase shell form construction. It is also to be understood that framing means (not shown) may be employed in association with the magnetic core 39 for clamping or restraining the laminations or the punchings included in the core 3% in position after the core has been assembled and stacked. It has also been found that the joints between the adjoining ends or edges of the laminations in each layer of the magnetic core 3% need not be perfectly closed for efiicient and satisfactory performance of the magnetic core 36. In the latter case, a slight separation upto one or two thicknesses of each lamination may be permissible.

It is to be noted that the core 3%? requires a minimum number of lamination shapes and the extending or projecting portions of the laminations at the outside of the overall core are efiectiveiy cooling fins which substantially increase the external surface cooling area of the core The latter feature may be of particular importance in certain applications.

Referring to FIG. 4, there is illustrated a second embodiment of a core and coil assembly 51 illustrating the teachings of this invention. In general, the core and coil assembly 5th includes a three-phase magnetic core St) of the core form type and three phase windings I dA, Fit-B and NBC disposed on said magnetic core and shown in dotted outline. The magnetic core 8t? which is of the I-plate type is similar to the magnetic core 39 except for the shape of the laminations which make up the core 3h. Similarly to the magnetic core 30, the magnetic core 8 includes a plurality of layers of laminations assembled in a substantialiy rectangular core around two substantially rectangular windows. T he magnetic core tit) is also divided into a pluraiity of groups of layers, each group comprising a plurality of layers of assembled laminations. Each layer of laminations of the magnetic core 8'59 includes first and second yoke laminations 38 and 98 respectively, first and second outer leg laminations 82 and 85 respectively, and a center leg lamination 34. As shown in PEG. 4, the laminations in each layer are assembled around two substantially rectangular windows with the adjoining edges of the substantially rectangular laminations in substantial alignment to form substantially perpendicular joints. Similarly to the groups of layers of lamie3 nations of the magnetic core 3%, the layers of laminations of the magnetic core 8t? are stacked in groups so that the ends of the corresponding laminations in successive layers overlap the ends of the laminations in the adjacent layers and are arranged in a stepped relation. it is to be understood that certain leg laminations included in the magnetic core fill may include extending portions (not shown) which would serve to interlock the leg laminations with the associated stacked yoke laminations.

The magnetic core Ell is particularly adapted for use with magnetic strip material which is either unoriented or which includes two preferred directions of orientation, one parallel to the longitudinal dimension of the magnetic strip material from which the laminations of the core are 7 formed and a second preferred direction substantially perpendicular to the longitudinal dimension of said magnetic strip material. ther features of construction of the mag netic core Si are similar to those of the magnetic core a 3i? shown in FIG. 1. For example, the extent of overlapping of the ends of the laminations should be a substantial amount, preferably at least six times the thickness of each lamination.

Referring to FIGS. and 6, there is illustrated a magetic core lllil showing a third embodiment of the invention. In general, the magnetic core 100 is similar to the magnetic core shown in FIG. 1 and includes a plurality of layers of laminations formed from a mag netic strip material having a preferred orientation length wise of said material. The layers of laminations are divided into groups, each including a plurality of layers of laminations assembled around a substantially rectangular window. Each layer of laminations includes at least two yoke laminations and two leg laminations assembled with the adjoining ends of the laminations substantially aligned to form diagonal joints.

In particular, the magnetic core lllil includes one or more groups of layers of laminations, such as the groups 129 and 130 shown in FIG. 6. Only the group 1% will be described in detail since the group 13% is identical to the group 12%. In this particular case, the group 120 includes a plurality of layers 101, 102, 103, MM and 195 which are shown in detail in FIG. 8. Each of the layers llll to 195 includes the first and second yoke laminations Ills and 124, 1134 and 144, 154 and 164, 174 and 134 and 194 and 2M, respectively, and first and second leg laminations 112 and 122, 132 and 142, 152 and 162, 172 and 132, and 192 and 202, respectively. The ends of the laminations which make up each layer of the magnetic core Hill are cut diagonally withrespect to the longitudinal dimension of the magnetic strip material from which the laminations are formed, preferably at an angle of substantially and at least one end of each yoke lamination also includes a portion which is cut substantially at a right angle to the longitudinal dimension of the magnetic strip material as indicated at 115 and 125 of the yoke laminations 114 and 124, respectively, of the first layer llll, shown in FIGS. 5 and 8.

The right angle or perpendicular cuts of the ends of the corresponding yoke iaininations in successive layers or" the magnetic core Hill are made in stepped relation as indicated in MG. 8 at 115, 137, 157 and 177 for the yoke laminations 114, 134-, 154, and 174, respectively, in the layers ldl to Mid, respectively. Since the leg laminations in ailthe layers of the magnetic core llltl are of the same size and shape, the diagonal joints between the laminations of each layer when assembled and stacked are overlapped by the ends of the laminations in the adjacent layers. It is to be noted that the perpendicular or normal cuts of the yoke laminations form substantially rectangular corners on at least one end of each yoke lamination which is located or disposed away from the window or" the core ltltl after the layers of magnetic core are assembled and stacked.

it is to be noted that the layers of laminations included in the group 124 are stacked with the rectangular corners 6 of the yoke laminations included in each layer substantially aligned so that the joints between the yoke laminations and the leg laminations included ineach layer of laminations are overlapped by asubstantial predetermined amount, preferably equal to or in excess of six times the thickness of each lamination. Referring to FIG. 7, it is to be noted that the dillerent group of layers of laminations 12% and hill included in the magnetic core 1% may be stacked in a recurring or repeating pattern as shown in FIG. 7 or with the slope of the stepped lap joints alternating in successive groups.

The magnetic core ill-ll possesses all. the advantages of the magnetic core 36 shown in FIG. 1 and also has several additional advantages. For example, the right angle cuts H5, and 137, and 157, 1'75 and 177, 195, 125, l lfl and 147, and 1&7, 18d and 137 and 2% of the yoke laminations, 114, 134, 154, 1'74, 194, 124, Md, 126d, lhd and Edd, respectively, of the group 12% provide a convenient surface at both ends of the magnetic core ltlil for applying a force or pressure during the stacking of the layers of laminations of the mag netic core 1%, either manually or by machine. In addition, the inner and outer surfaces of the laminations which make up the layers of laminations in each group provide substantially flat surfaces on the inside and on the outside of the magnetic core ill-t} for supporting an electrical winding (not shown) which would be disposed on the magnetic core Hill.

It is to be understood that a core constructed as dis closed in M68. 5 and 6 may alsoinclude center leg iaminations which would be similar to the center leg laminations shown in FIG. 20, which will be described in detail hereinafter, and that the joint between such center leg laminations and the associated yoke laminations' would require a generally V shaped recess in each of said yoke laminations. For example, FIG. 5A illustrates the core of FIG. 5 with a center leg lamination 312' similar to the laminations shown in FIG. 20. Laminations in FIG. 5A which are similar to laminations in FIGS. 5 and 20 are indicated with like referencenumerals and prime marks. Lamination 115 of FIG. 5 is shown as two pieces, 115? and 115" in FIG. 5A, to illustrate that either lamination 115 or I24, or both, may be constructed of more than one piece. It is to be noted that the magnetic core Hill has a further advantage in that positioning holes may not be necessary in order to establish the stepped relation of the joints in the diftent layers of laminations. It should be noted that in a particular application, the width of the yoke laminations in any of the core constructions disclosed may be varied to make the width of the yoke laminations greater than the width of the associated leg laminations in order to obtain a more desirable magnetic characteristic of the overall magnetic core.

Referringto M63. 9 and ii, there is illustrated a fourth embodiment of a magnetic core illustrating the teachings of this invention. In general, the magnetic core 2% is similar to the magnetic core lilh and includes a plurality of layers of laminations formed from a magnetic strip material having a preferred orientation lengthwise of said material. The magnetic core Ztld includes one or more groups of layers of laminations such as the groups 2% and 239 shown in FIG. ll, each including a plurality of layers of assembled laminations. The chief difference between the magnetic core Ztill and the magnetic core ltld is that at least one end of both the yoke laminations and the leg laminations included in the core Zilhhas a portion cut substantially perpendicular to the longitudinal dimension of the magnetic strip material from which said laminations are formed rather than having only one end of each of the yoke laminations cut with a portion which is normal to the longitudinal dimension of the strip material.

Since the groups 22d and 23% are identical, only the group 22% will be described in detail. The group 22% includes the plurality of layers of laminations 2191 to 2M, as shown in FlG. 10. The layers Zill to can inclusive include the first and second yoke laminations 2M and 224, 234 and 244-, 254i and 264, and 274- and 284, respectively, and first and second leg laminations 212 and 222, 232 and 2 2, 252 and 262, and 272 and 282., respectively. The ends of each of the laminations included in the magnetic core 2% are at least partially cut diagonally with respect to the longitudinal dimension of the magnetic strip material from which the laminations are formed and at least one end of each of said laminations also includes a portion which is cut substantially perpendicular to the longitudinal dimension of said material to form at least one substantially rectangular corner on each of said laminations. The perpendicular cuts in said laminations are staggered or offset in successive layers as shown in FIG. so that the ends or the diagonal joints between the adjoining ends or edges of the laminations in each of said layers are overlapped by a portion of the corresponding laminations in the adjacent layers as shown in FIGS. 9 and 11. When the layers of laminations are stacked with the rectangular corners of the laminations substantially aligned on the outside of the core 2%, a series of lap joints are formed in stepped relation as shown in FIGS. 11 and 12. The extent of the overlapping of the ends of each lamination by the ends of the corresponding laminations in the adjacent layers is preferably at least six times the thickness of each lamination.

Referring to FIG. 12, the stepped-lap joints in each of the groups 229 and 23% may be arranged to form a recurring or repeating pattern as shown, with the slope of the overall stepped-lap joint in each group being the same. An alternative construction of the magnetic core 2% is shown in FIG. 13 with a second group of layers of laminations 2% having the laminations reversed during assembly and stacking to form with the first group 220 an overall stepped-lap joint which includes eight steps rather than a repeated four-step joint as shown in P16. 12.

The diagonal joints between the laminations of adjacent successive layers in the alternative overall joint would be substantially symmetrically disposed with respect to a diagonal reference line extending from a corner of the overall window of the alternative core to the nearest outer corner of the latter overall core.

It is to be understood that the magnetic core 2% may be employed in different forms similarly to the magnetic core Tilt! as previously discussed. For example, the construction disclosed in FIGS. 9 through 13 may be employed in a three-phase core of the core-form type, as illustrated in FIG. 9A, including a center leg lamination in each of the layers of laminations. Laminations in PEG. 9A which are similar to laminations in FIGS. 9 and 20, are indicated with like reference numerals and prime marks.

The magnetic core 2% possesses all the magnetic advantages of the magnetic core 1th? and has the additional advantage that both the leg laminations and the yoke laminations each includes a rectangular corner against which force or pressure may be applied during the assembly and the stacking of the core Edi-ti either by machine or manually. This means that the corresponding yoke or leg laminations of the respective layers may be prestacked to facilitate assembly of the overall core 2% or that either the yoke or leg laminations may be aligned against a stop or wall to facilitate assembly of the core 2%.

Referring to FIG. 14, there is illustrated a fifth embodiment of a magnetic core illustrating the teachings of this invention. In general, the core and coil assembly includes the magnetic core sections 31A and Edi-B and the electrical windings 32th, 320 and 33% disposed on said t? magnetic core sections. The magnetic core sections SMA and 3MB together form a three-phase magnetic core of the shell-form type, having a substantially rectangular overall shape and including six substantially rectangular windows. It is to be understood that the construction disclosed in FIG. 14 may be adapted to a three-phase coreform type construction.

In particular, the magnetic core section EMA includes a plurality of layers of laminations formed from a magnetic strip material having a preferred orientation length wise of said material and assembled around three substantially rectangular windows. The layers of laminations are divided into a plurality of groups 349 and 359 as shown in FIG. 15 each of said groups including a plurality of layers of laminations.

In particular, the top layer of laminations of the magnetic core section BillilA includes first and second outer yoke liminations 3th; and 308, first and second intermediate yoke laminations 312 and 314, a center leg lamination 3% and an outer leg lamination 304. Similarly, the top layer of laminations of the magnetic core section 3018 includes first and second outer yoke laminations 322 and 328, first and second intermediate yoke laminations $32 and 334, a center leg lamination 32 i and an outer leg lamination 3.26. The ends of the intermediate yoke laminations 312, 314, 332 and 33 are cut to be genenally V-shaped as indicated at Sill and 313, 315 and 317, 331 and 333 and 335 and 337, respectively. Each of the leg laminations 394, 3%, 324 and 326 includes two gen erally V-shaped recesses to accommodate the ends of the associated intermediate yoke laminations 312, 31-4, 332 and 334. The ends of the leg laminations 3M, 3%, 324 and 326 are cut diagonally with respect to the longitudirial dimension of the magnetic strip material from which they are formed, preferably at an angle of substantially 45. The ends or" the outer yoke laminations sea, 3%, 322 and 328 are either entirely or partially cut diagonally with respect to the longitudinal dimension of the magnetic strip material from which said laminations are formed, preferably at an angle of substantially 45. At least one end of each of the yoke laminations included in the magnetic core sections 391A and 3018 is cut substantially perpendicular to the longitudinal dimension of the magnetic strip material from which said laminations are formed to provide a substantially rectangular corner on each of said outer yoke laminations.

The cut ends of the corresponding outer yoke laminations and the intermediate yoke laminations are made in stepped relation in successive layers of the magnetic core sections 3432A and 391B, as indicated in FIG. in detail, for the intermediate yoke lamination 312 of the magnetic core section 3531A. The generally ti-shaped ends of the intermediate yoke laminations 312A to 312D inclusive in four successive layers of laminations are cut in stepped relation as shown in FIG. 20 in what might be described as a staggered or ofiset relationship. Therefore, when the laminations which make up each layer of laminations of the group 34d of the magnetic core section SEPTA are assembled with the adjoining ends or edges of the laminations substantially aligned to form diagonal joints and the successive layers of laminations are stacked with the rectangular corners of the outer yoke laminations substantially aligned, the ends of each lamination are overlapped by the ends of the corresponding laminations in the adjacent layers as shown in FIG. 14 and FIG. 15. The rectangular corners of the outer yoke laminations provide convenient surfaces against which force or pressure may be applied during the assembly and the stacking of the layers of laminations which comprise the magnetic core sections TitlilA and 3MB.

Referring to FIG. 15, the groups 340 and 35% which make up the magnetic core section ItllA may be stacked in a recurring or repeating pattern as shown in FIG. 15 or arranged with the laminations reversed in a second group 37%? as shown in FIG. 16, in which the slopes of the stepped-lap joints formed in the first group 340 and in the second group 376 are arranged to be in opposite directions. Similarly to the cores 30, 100 and 2% previously discussed, the extent of the overlapping of the ends of the laminations by the ends of the corresponding laminations in the adjacent layers of the core 300 should be a substantial amount, preferably at least six times the thickness of each lamination. The stepped-lap joints formed in each group of layers of laminations of the magnetic core sections 3ii1A and 3013 should extend through a substantial portion of the thickness of the overall magnetic core sections 301A and 301B, preferably through at least six layers. It should be noted that the center leg laminations of the magnetic core sections 301A and 301B form a center leg portion in the magnetic core 300 having a width which is substantially twice the width of the outer leg portions of the magnetic core 3%, as required for a single phase core ofthe shell-form type. It is also to be noted that the width of the outer yoke laminations of the magnetic core sections 301A and 361B is greater'than the width ofthe associated leg laminations of said magnetic core sections in order to obtain a more desirable magnetic performance of the overall magnetic core 390. An alternative construction of the magnetic core 300 wouldinclude outer yoke laminations, such as the outer yoke lamination 408 shown in FIG. 17, having substantially the same width as the associated leg laminations 404 and 426.

Referring to FIGS. 18 and 19, another alternative construction of the magnetic core Still would include outer yoke laminations, such as the outer yoke lamination .428, and associated leg laminations 414 and 436 shown in FIG. 18, all having at least one end with a portion cut substantially perpendicularly to the longitudinal dimension of the magnetic strip material from which said laminations are formed. The latter construction is similar in general to the construction of the magnetic core 200 shown in FIGS. 9 through 13 in that the rectangular corners provided by the perpendicular cuts on each lamination permit the application of force or pressure during assembly of a magnetic core similar to the magnetic core.

300 shown in FIG. 14 or the alignment of said laminations against a flat surface or stop during assembly, either by machine or manually. As shown in FIGS. 18 and 19, a magnetic core 400 may include one or more groups, such as the groups 430 and 440 shown in FIG. 19, with the layers of laminations of the respective groups stacked to form repeating or recurring stepped-lap joints in each of said groups having the same slope direction or the laminations in a second group 460 as shown in FIG. 21 may be reversed with respect to the laminations in the first group 430 to provide an overall stepped-lap joint at the corners having twice the number of steps in the overall stepped-lap joint. The diagonal joints between the laminations of each of theadjacent successive layers in the alternative overall joint would be substantially symmetrically disposed with respect to a diagonal reference line extending from a corner of the overall window ofthe alternative core to the nearest outer corner of the latter overall core.

The magnetic cores 200, 300, and 4% each possess advantages similar to those of the magnetic core 1% shown in FIGS. and 6 in that each of said cores provides flat surfaces both on the inside windows of said cores and on the outside of the overall assembled cores which provide firm support for associated electrical windings disposed on said cores and minimizing the possi-' bility of any damage to said electrical windings during assemblyof an overall time and coil assembly. In addi tion, the magnetic cores 100, 200, Mill and 400 share a common advantage in that positioning holes or recesses are probably not required to obtain a stepped-lap joint in each of the groups of layers of laininations which make up each of said cores.

It is to be understood thatthe thickness and width of the magnetic strip material from which the laminations of j the various cores disclosed are formed may be varied as required by the necessary capacity or" the final assembled core and the dimensions of the preformed windings with which said cores are normally assembled. It is also to be understood that the number of steps in the stepped-lap joint provided in each group of layers of laminations of a core as disclosed may be varied in a particular application and that different groups of layers may include a different number of layers of laminations for reasons of magnetic design or otherwise. In addition, the overall shape of the magnetic core embodying the teachings of this invention may be other than that of the substantially rectangular-shaped cores as disclosed in a particular application. It is to be understood that the laminations of a magnetic core as disclosed may be further divided into a larger number of laminations in each layer in a particular application to provide additional stepp'eddap joints in a particular core, while still embodying the teachings of this invention.

The apparatus embodying the teachings of this invention has several advantages. For example, the exciting current and the, associated losses have been found to be less than those of a conventional magnetic core of the same general type; In addition, magnetic cores of the type disclosed lend themselves to convenient assembly and stacking by machine methods during manufacture and certain of the cores disclosed provide unusually good support for the electrical windings which are normally disposed on said cores. Further it has been found that the eifective air gaps in, the joints of a magnetic core as disclosed are reduced and the noise level associated with said cores is also reduced. It is to be noted that during assembly of the laminations and the stacking of the layers of laminations that several corresponding laminations in successive layers may be assembled or stacked simultaneously to facilitate stacking of a core constructed in accordance with the invention.

Since numerous changes may be. made in the above described apparatus and diiferent embodiments of the invention may be made without departing from the spirit thereof, it is intended that .all the matter contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative, and not in i a limiting sense. 1

We claim as our invention:

1. In a magnetic core, the combination comprising a plurality of layers of laminations formed from a magnetic strip material having a preferred orientation lengthwise of said strip material, each of said layers including at least four laminations assembled around a substantially rectangular window and forming four outer corners, the adjoining ends of said laminations in each of said layers being substantially aligned to form diagonal joints, said laminations having ends sheared diagonally with respect to the longitudinal dimension of said strip mate rial with at least one end of two of said laminations also including a portion clipped substantially perpendicular to the longitudinal dimension of said strip material to form a substantially rectangular corner, the perpendicular portions of said clipped lamination being arranged in stepped relation in successive layers forming a stepped pattern on one side of each outer corner of said magnetic core, said stepped pattern being formed by stepping at least three successive'layers of said laminations in the same direction, said layers being stacked with the rectangular corners'of said clipped laminations substantially aligned and the ends of said laminations overlapping the joints be-' lar Window and forming four substantially squared outer corners, the adjoining ends of said laminations in each of said layers being substantially aligned to form diagonal joints, the ends of each of said laminations being cut diagonally with respect to the sides of said strip material and at least one end of each yoke lamination also including a portion cut substantially perpendicular to the sides of said strip material to form a substantially rectangular corner on each yoke lamination, said layers of laminations being divided into groups each including a plurality of layers, the perpendicularly cut ends of the yoke laminations in each group being cut in stepped rela tion in successive layers forming a stepped pattern on one side of each outer corner of said magnetic core, said stepped pattern being formed by stepping at least three successive layers of said laminations in the same direction, the layers of each group being stacked with the rectangular corners of said yoke laminations substantially aligned and the ends of the laminations in each layer overlapping the ends of the laminations in the adjacent layers.

3. In a magnetic core, the combination comprising a plurality of layers of laminations formed from a magnetic strip material having a preferred orientation parallel to the sides of said strip material, each layer including at least two yoke laminations and two leg laminations assembled around a substantially rectangular window and forming four substantially squared outer corners, the adjoining ends of said laminations in each of said layers being substantially aligned to form diagonal joints, the ends of each of said laminations being cut diagonally with respect to the sides of said strip material .and at least one end of each yoke lamination also including a portion cut substantially perpendicular to the sides or" said strip material to form a substantially rectangular corner on each of said yoke laminations, said layers of laminations being divided into groups each including a plurality of layers, the perpendicular cut ends of the yoke laminations in each group being cut in stepped relation in successive layers forming a stepped pattern on one side of each outer corner of said magnetic core, said stepped pattern being formed by stepping at least three successive layers of said laminations in the same direction, the layers of each group being stacked with the rectangular corners of said yoke laminations substantially aligned and the ends of the laminations in each layer overlapping the ends of the laminations in the adjacent layers, said groups being arranged with the joints between the laminations of the layers of each group forming a recurring pattern.

4. In a magnetic core, the combination comprising, a plurality of layers of laminations formed from a magnetic strip material having a preferred orientation parallel to the sides of said strip material, each layer including at least two yoke laminations and two leg laminations assembled around a substantially rectangular window and forming four substantially squared outer corners, the adjoining ends of said laminations in each of said layers being substantially aligned to form diagonal joints, the ends of each of said laminations being cut diagonally with respect to the sides of said strip material and at least one end of each yoke lamination also including a portion cut substantially perpendicular to the sides of said strip material to form a substantially rectangular corner on each of said yoke laminations, said layers of laminations being divided into groups each including a plurality of layers, the perpendicularly cut ends of the yoke laminations in each group being cut in stepped relation in successive layers forming a repeating stepped pattern on one side of each outer corner of said magnetic core, said stepped pattern being formed by stepping at least three successive layers of said laminations in the same direction, the layers of each group being stacked with the rectangular corners of said yoke laminations substantially aligned and the ends of the laminations in each layer overlapping the ends of the laminations in the adjacent layers, said groups being arranged with the joints between the laminations of the layers of each group forming a recurring pattern, the extent of the overlapping of the ends of each of the laminations by the ends of the laminations in the adjacent layers being at least six times the thickness of each lamination.

5. In a magnetic core, the combination comprising, a plurality of layers of laminations formed from a magnetic strip material having a preferred orientation parallel to the sides of said strip material, said layers each including at least two yoke laminations and two leg laminations assembled around a substantially rectangular window and forming four outer corners, the adjoining ends of the said laminations in each of said layers being substantially aligned to form diagonal joints, the ends of said yoke and leg laminations being cut diagonally with respect to the sides of said strip material and at least one end of each of said laminations including a portion cut at substantially a ri ht angle with respect to sides of said strip material to form a substantially rectangular corner, the right angle cuts of said laminations being made in a stepped relation in successive layers forming a stepped pattern on one side of each outer corner of said magnetic core, said stepped pattern being formed by stepping at least three successive layers of said laminations in the same direction, said layers being stacked with the rectangular corners of said laminations substantially aligned and with the ends of each of said laminations overlapping the joints between the ends of the laminations in the adjacent layers.

6. In a magnetic core, the combination comprising, a plurality of layers of laminations formed from a magnetic strip material having a preferred orientation parallel to the sides of said material, each of said layers including at least two yoke laminations and two leg laminations assembled around a substantially rectangular window and forming four substantially squared outer corners, the adjoining ends of said laminations being substantially aligned to form diagonal joints, the ends of each of said laminations being cut diagonally with respect to the sides of said strip material and at least one end of each lamination including a portion cut substantially normal to the sides of said strip material to form a substantially rectangular corner on each lamination, said layers of laminations being divided into groups, each of said groups including a plurality of layers, the normal cuts of the ends of said laminations being made in stepped relation in successive layers forming a stepped pattern on one side of each outer corner of said magnetic core, said stepped pattern being formed by stepping at least three successive layers of said laminations in the same direction, the layers of each group being stacked with the rectangular corners of said laminations substantially aligned and the ends of each of the laminations in each layer overlapping the ends of the corresponding laminations in the adjacent layers.

7. In a magnetic core, the combination comprising, a plurality of layers of laminations formed from a magnetic strip material having a preferred orientation parallel to the sides of said material, each of said layers including at least two yoke laminations and two leg laminations assembled around a substantially rectangular window and forming four substantially squared outer corners, the adjoining ends of said laminations being substantially aligned to form diagonal joints, the ends of each of said laminations being cut diagonally with respect to the sides of strip material and at least one end of each lamination including a portion out substantially normal to the sides of said strip material to form a substantially rectangular corner on each lamination, said layers of laminations being divided into groups, each of said groups including a plurality of layers, the normal cuts of the ends of said laminations being made in stepped relation in successive layers forming a repeating stepped pattern on one l3 side of each outer corner of said magnetic core, said stepped pattern being formed by stepping at least three successive layers of said laminations in the same direction, the layers of each group'being stacked with the rectangular corners of said laminations substantially aligned and the ends of the laminations in each layer overlapping the ends of the laminations in the adjacent layers, the extent of the overlapping of the ends of each of said laminations by the ends of the laminations in the adjacent layers being at least six times the thickness of each lamination.

8. A three-phase magnetic core of the shell form type, comprising two similar core sections, each core section having a plurality of layers of laminations formed from magnetic strip material having a preferred orientation parallel to the sides of said material, each layer of each cone section including four outer and two intermediate laminations, assembled around three substantially rectangular windows forming four outer corners, the adjoining edges of said laminations being substantially aligned to form diagonal joints, the ends of said intermediate laminations being cut in substantially a V-shape, the ends of said outer laminations being cut diagonally with respect .to the sides of said strip material, two of said laminations each including two generally V-shaped recesses to accommodate the ends of said intermediate laminations, at least one end of two of said outer laminations also including a portion cut substantially perpendicularly with respect to the sides of said strip, material to form a substantially rectangular corner, the cuts and recesses of said laminaions being made in stepped relation insuccessive layers forming a stepped pattern, the stepped pattern at the intersection of said outer laminations being on one side of each outer corner of said core sections, said stepped pattern being formed by stepping at least three successive layers of said laminations in the same direction, said layers being stacked with the rectangular corners of said outer yoke laminations substantially aligned and portions of each of said laminations overlapping the ends of the laminations in the adjacent layers, said core sections being disposed with one of the legs of one core section adjacent one of the legs of the other core section, said adjacentlegs forming an inner leg of said three phase magnetic core.

9. A three-phase magnetic core of the shell form type comprising two similar core sections, each core section having a plurality of layers of laminations formed from magnetic strip material having a preferred orientation parallel to the sides of said material, each layer of each said core section including two outer and two intermediate yoke laminations, and two leg laminations assembled around three substantially rectangular windows and forming tour substantially squared outer corners, the adjoining edges of said laminations being substantially aligned to form diagonal joints, the ends of said intermediate yoke laminations being cut in substantially a V-shape, the ends of the outer yoke laminations and the leg laminations being cut diagonally with respect to the sides of said strip material, said leg laminations each including two generally V-shaped recesses to accommodate the ends of said intermediate yoke laminations, at least one end of each outer yoke lamination also including a portion cut substantially normal to the sides of said strip material to form a substantially rectangular corner on each outer yoke lamination, said layers of laminations in each core section being divided into groups, each of said groups including a plurality of layers, the cuts and the recesses of the laminations of the layers in each group being made in stepped relation in successive layers forming a stepped'pattern, the stepped pattern at the intersection of said outer yoke and leg laminations being on one side of each outer corner of said core sections, said stepped pattern being formed by stepping at least three successive layers of said laminations in the same direction, the layers of each group being stacked with the rectangular corners of said outer yoke'laminations substantially aligned and portions of each of said laminations overlapping the ends of the laminations in the adjacent layers, said core sectionsbeing disposed with one of the legs of one core section adjacent one of the legs of the other core section, said adjacent legs forming an inner leg of said three phase magnetic core.

10. A three-phase magnetic core of the shell form type comprising a first and second core section, said first and second core sections each having a plurality of layers of laminations formed from magnetic strip material having a preferred orientation parallel to the sides of said material, each layer of saidfir'st and second core sections each including two outer and two intermediate yoke laminations, and 'two leg laminations being assembled around three substantially rectangular windows and joining edges of said laminations being substantially forming four substantially squared outer corners, the ad aligned to form diagonal joints, the ends of said intermediate yoke laminations being cut in substantially'a V-shape, the ends of the outer yoke laminations and the leg laminations being cut diagonally with respect to the sides of said strip material, said leg laminations each including two generally V-shaped recesses to accommodate the ends of said intermediate yoke laminations, at least one end of each outer yoke lamination also including a portion cut substantially normal to the sides of said strip material to form a substantially rectangular corner on each outer yoke lamination, said layers of laminations said first and second core sections being divided into groups, each of said groups including a plurality of layers, the cuts and recesses of the laminations of the layers in each group being made in stepped relation in successive layers forming a repeating stepped pattern, the stepped pattern at the intersection of said outer yoke and leg laminations being on one side of each corner of said first and second core sections, said stepped pattern being formed by stepping at least three successive layers of said laminations in the same direction, the layers of each group being stacked with the rectangular corners of said outer yoke laminations substantially aligned and portions of each of said laminations overlapping the ends of the laminations in the adjacent layers, the extent of the overlapping of the ends of each lamination by portions of the laminations in the adjacent layers being at least six times thet-hickness of each lamination, said first and second core sections being disposed with one of the legs of said first core section adjacent one of the legs of said second core section, said adjacent legs forming an inner leg of said three phase magnetic core.

11. A three-phase magnetic core of the shell form type comprising two similar core sections, each core section having a plurality of layers of laminations formed from magnetic strip material having a preferred orientation parallel to the sides of said material, each layer of each said core section including two outer and two intermediate yoke laminations, and two two leg laminations assembled around three substantially rectangular windows and forming four substantially squared outer corners, the adjoining edges of said laminations being substantially aligned to form diagonal joints, the ends of said intermediate yoke laminations being cut in substantially a V-shape, the ends of the outer yoke laminations and the leg laminations being cut diagonally with respect to the sides of said strip material, said leg laminations each including two generally V-shaped recesses to accommodate the ends of said intermediate yoke laminations, at least one end of each of said leg and outer yoke laminations also including a portion cut at substantially a right angle to the sides of said strip material to form a substantially rectangular corner on each of said leg and outer yoke laminations, the cuts and recesses of said laminations being made in stepped relation in successive layers forming a stepped pattern, the stepped pattern at the intersection of said outer yoke and leg laminations being on one side 8,1 iii of each corner of said core sections, said stepped pattern being formed by stepping at least three successive layers of said laminations in the same direction, said layers of laminations being stacked with the rectangular corners of said leg and outer yoke larninations substantially aligned and portions of each of said laminations overlapping the ends of the laminations in the adjacent layers, said core sections being disposed with the leg of one core section adjacent the leg of the other core section, said adjacent legs forming an inner leg of said three phase magnetic core.

12. A three-phase magnetic core of the shell form type having two similar sections each comprising a plurality of layers of laminations formed from magnetic strip material having a preferred orientation parallel to the sides of said material, each layer including two outer and two intermediate yoke laminations, and two leg laminations assembled around three substantially rectangular windows and forming four substantially squared outer corners, the adjoining edges of said laminations being substantially aligned to form diagonal joints, the ends of said intermediate yoke laminations being cut in substantially a V-shape, the ends of the outer yoke laminations and the leg laminations being cut diagonally with respect to the sides of said strip material, said leg laminations each including two generally V-shaped recesses to accommodate the ends of said intermediate yoke laminations, at least one end of each of said leg and outer yoke laminations also including a portion cut at substantially a right angle to the sides of said strip material to form a substantially rectangular corner on each of said leg and outer yoke laminations, said layers of laminations being divided into groups, each of said groups including a plurality of layers, the cuts and recesses of said laminations being made in stepped relation in successive layers of each group forming a stepped pattern, the stepped pattern at the intersection of said outer yoke and leg laminations being on one side of each corner of said core sections, said stepped pattern being formed by stepping at least three successive layers of said laminations in the same direction, said layers of laminations of each group being stacked with the rectangular corners of said leg and outer yoke laminations substantially aligned and portions of each of said laminations of the layers in each group overlapping the ends of the laminations in the adjacent layers, said core sections being disposed with the leg of one core section adjacent the leg of the other core section, said adjacent legs forming an inner leg of said three phase magnetic core.

13. A three phase magnetic core of the shell form type having two similar sections each comprising, a plurality of layers of laminations formed from magnetic strip material having a preferred orientation parallel to the sides of said material, each layer including two outer and two intermediate yoke laminations, and two leg laminations assembled around three substantially rectangular Windows and forming four substantially squared outer corners, the adjoining edges of said laminations being substantially aligned to form diagonal joints, the ends of said intermediate yoke laminations being cut in substantially a V-shape, the ends of the outer yoke laminations and the leg laminations being cut diagonally with respect to the sides of said strip material, said leg laminations each including two generally V-shaped recesses to accommodate the ends of said intermediate yoke laminations, at least one end of each of said leg and outer yoke lamination also including a portion cut at substantially a right angle with respect to the sides of said strip material to form a substantially rectangular corner on each of said leg and outer yoke laminations, said layers of laminations being divided into groups, each of said groups includin a plurality of layers, the cuts and recesses of said laminations in the layers of each group being made in stepped relation in successive layers of each group forming a stepped pattern, the stepped pattern at the intersection of said outer yokes and leg laminations being on one side of each corner of said core sections, said stepped pattern being formed by stepping at least three successive layers of said laminations in the same direction, said layers of laminations of each group being stacked with the rectangular corners of said leg and outer yoke laminations substantially aligned and portions of each of said laminations overlapping the ends of the laminations in the adjacent layers, the extent of the overlapping of the ends of said laminations by portions of the laminations in the adjacent layers of each group being at least six times the thickness of each lamination, said core sections being disposed with one of the legs of one core section adjacent one of the legs of the other core section, said adjacent legs forming an inner leg of said three phase magnetic core.

14. A magnetic core comprising a plurality of layers of laminations formed from magnetic strip material having a preferred orientation lengthwise of said strip material, each of said layers including at least four outer laminations and one inner lamination assembled around two substantially rectangular windows and forming four outer corners, the adjoining ends of the laminations in each layer being substantially aligned to form diagonal joints, said outer laminations having ends sheared diagonally with respect to the longitudinal dimension of said strip material with at least one end of two of said laminations also including a portion clipped substantially perpendicular to the longitudinal dimension of said strip material to form a substantially rectangular corner, the inner lamination having each end sheared in substantially a V shape, the perpendicular portions of said clipped laminations being arranged in stepped relation in successive layers forming a stepped pattern on one side of each outer corner of said magnetic core, said stepped pattern being formed by stepping at least three successive layers of said laminations in the same direction, said layers being stacked with the rectangular corners of said clipped laminations substantially aligned and the ends of said laminations overlapping the joints between the ends of the laminations in the adjacent layers.

15. A magnetic core comprising a plurality of layers of laminations formed from a magnetic strip material having a preferred orientation parallel to the sides of said strip material, each layer including a plurality of upper and lower yoke laminations and two outer and one inner leg laminations assembled around two substantially rectangular windows and formingiour substantially squared outer corners, the adjoining ends of the laminations in each layer being substantially aligned to form diagonal joints, the ends of each of said laminations being cut diagonally with respect to the sides of said strip material, the inner leg lamination having each end cut in substantially a ii-shape, said plurality of upper and lower yoke laminations being cut to provide recesses shaped to receive the ends of said inner leg member, at least one end of each of said upper and lower yoke laminations also including a portion cut substantially perpendicular to the sides of said strip material to form a substantially rectangular corner on each yoke lamination, said layers of laminations being divided into groups each including a plurality of layers, the perpendicularly cut ends of the yoke laminations in each group being cut in stepped relation in successive layers forming a stepped pattern on one side of each outer corner of said magnetic core, said stepped pattern being formed by stepping at least three successive layers of said laminations in the same direction, the layers of each group being stacked with the rectangular corners of said yoke laminations substantially aligned and the ends of the laminations in each layer overlapping the ends of the laminations in the adjacent layers.

16. A magnetic core comprising a plurality of layers of laminations formed from a magnetic strip material having a preferred orientation parallel to the sides of said strip material, each layer including at least two upper yoke laminations and a lower yoke lamination and three leg laminations assembled around two substantially rectangular windows and forming four substantially squared outer corners, the adjoining ends of the laminations in eachlayer being substantially aligned to form diagonal joints, the ends of each of said laminations being cut diagonally with respect to the sides of said strip material and at least one end of each yoke lamination also including aportion cut substantially perpendicular to the sides of said strip material to form a substantially rectangular corner on each yoke lamination, the inner leg lamination having each end cut in substantially a V-shape, said upper and lower yoke laminations being cut to provide recesses shaped to receive the ends of said inner leg lamination, said layers of laminations being divided into groups each including a plurality of layers, the perpendicularly cut ends of the yoke laminations in each group being cut in stepped relation in successive layers forming a stepped pattern on one side of each outer corner of said magnetic core, said stepped pattern being formed by stepping at least three successive layers of said laminations in the same direction, the layers of each group being stacked with the rectangular corners of said yoke laminations substantially aligned and the ends of the laminations in each layer overlapping the ends of the laminations in the adjacent layers.

17. A magnetic core comprising a plurality of layers of laminations formed from a magnetic strip material having a preferred orientation parallel to the sides of said strip material, each layer including at least two yoke laminations and two outer and one inner leg laminations assembled around two substantially rectangular windows and forming four substantially squared outer corners, the adjoining ends of the laminations in each layer being substantially aligned to form diagonal joints, the ends of each of said laminations being cut diagonally with respect to the sides of said strip material and at least one end of each yoke lamination also including a portion cut substantially perpendicular to the sides of said strip material to form a substantially rectangular corner on each of said yoke laminations, the inner leg lamination having each end cut in substantially a V-shape, said yoke laminations being cut to provide recesses shaped to receive the ends of said inner leg lamination, said layers of laminations being divided into groups each including a plurality of layers, the perpendicularly cut ends of the yoke laminations in each group being cut in stepped relation in successive layers forming a stepped pattern one one side of each outer corner of said magnetic core, said stepped pattern being formed by stepping at least three successive layers of said laminations in the same direction, the layers of each group being stacked with the rectangular corners of said yoke laminations substantially aligned and the ends of the laminations in each layer overlapping the ends of the laminations in the adjacent layers, said groups being arranged with the joints between the laminations of the layers of each group forming a recurring pattern.

18. A three phase magnetic core of the core form type comprising, a plurality of layers of laminations formed from a magnetic strip material having a preferred orientation parallel to the sides of said strip material, each layer including at least two yoke laminations and two outer and one inner leg laminations assembled around two substantially rectangular windows and forming four substantially squared outer corners, the adjoining ends of the laminations in each layer being substantially aligned to form diagonal joints, the ends of each of said laminations being cut diagonally with respect to the sides of said strip material, the ends of the inner leg lamination being additionally cut to form a substantially V-shape, said yoke laminations being cut to provide recesses shaped to receive the ends of said inner leg lamination, at least one end or" each yoke lamination also including a portion cut substantially perpendicular to the sides of said strip material to form a substantially rectangular corner on each of said yoke laminations, said layers of laminations being divided into groups each including a plurality of layers, the perpendicularly cutends of the yoke laminations in each group being cut in stepped relation in successive layers forming a stepped pattern on one side of each outer corner of said magnetic core, said stepped pattern being formed by stepping at least three successive layers of said laminations in the same direction, the layers of each group being stacked with the rectangular corners of said yoke laminations substantially aligned and the ends of the laminations in each layer overlapping the ends of the laminations in the adjacent layers, said groups being arranged with the joints between the laminations of the layers of each group forming a recurring pattern, the extent of the overlapping of the ends of each of the laminations by the ends of the laminations in the adjacent layers being at least six times the thickness of each lamination.

19. A magnetic core comprising, a plurality of layers of laminations formed from a magnetic strip material having a preferred orientation parallel to the sides of said strip material, said layers each including at least two yoke laminations and two outer and one inner leg laminations assembled around two substantially rectangular windows and forming four substantially squared outer corners, the adjoining ends of the laminations in each layer being substantially aligned to form diagonal joints, the ends of said inner leg being cut to form substantially a V-shape, said yoke laminations being cut to provide recesses shaped to receive the ends of said inner leg lami nation, the ends of said yoke and outer leg laminations being cut diagonally with respect to the sides of said strip material and at least one end of each of said yoke and outer leg laminations including a portion cut at substantially a right angle with respect to the sides of said strip material to form a substantially rectangular corner, the right angle cuts of said laminations being made in a stepped relation in successive layers forming a stepped pattern on one side of each outer corner of said magnetic core, said stepped pattern being formed by stepping at least three successive layers of said laminations in the same direction, said layers being stacked with the rectangular corners of said laminations substantially aligned and with the ends of each of said laminations overlapping the joints between the ends of the laminations in the adjacent layers.

20. A magnetic core comprising a plurality of layers of laminations formed from a magnetic strip material having a preferred orientation parallel to the sides of said strip material, said layers each including at least two upper and two lower yoke laminations and two outer and one inner leg laminations assembled around two substantially rectangular windows and forming four substantially squared outer corners, the adjoining ends of the laminations in each layer being substantially aligned to form diagonal joints, the ends of said inner leg being cut to form a substantially V-shape, said upper and lower yoke laminations being cut to provide recesses when assembled which will receive the ends of said inner leg lamination, the ends of said yoke and outer leg laminations being cut diagonally with respect to the sides of said strip material and at least one end of each of said yoke and outer leg laminations including a portion cut at substantially a right angle with respect to the sides of said strip material to form a substantially rectangular corner, the right angle cuts of said laminations being made in a stepped relation in successive layers forming a stepped pattern on one side of each outer corner of said magnetic core, said stepped pattern being formed by stepping at least three successive layers of said laminations in the same direction, said layers being stacked with the rectangular corners of said laminations substantially aligned and with the ends of each of said laminations 1?? overlapping the joints between the ends of the laminations in the adjacent layers.

21. A magnetic core comprising, a plurality of layers of laminations formed from a magnetic strip material having a preferred orientation parallel to the sides of said material, each of said layers including at least two upper and one lower yoke laminations and two outer and one inner leg laminations assembled around two substantially rectangular windows and forming four substantially squared outer corners, the adjoining ends of said laminations being substantially aligned to form diagonal joints, the ends of the inner leg lamination being cut to form substantially a V-shape, said upper yoke laminations being cut to provide a recess when assembled which will receive one end of said inner leg lamination, said lower yoke lamination being cut to provide a recess to receive the remaining end of said inner leg lamination, the ends of each of said yoke and outer leg laminations being cut diagonally with respect to the sides of said strip material and at least one end of each of said yoke and outer leg laminations including a portion cut substantially normal to the sides of said strip material to form a substantially rectangular corner on each of said yoke and outer leg lamination, said layers of laminations being divided into groups, each of said groups including a plurality of layers, the normal cuts of the ends of said yoke and outer leg laminations being made in stepped relation in successive layers forming a stepped pattern on one side of each outer corner of said magnetic core, said stepped pattern being formed by stepping at least three successive layers of said laminations in the same direction, the layers of each group being stacked with the rectangular corners of said yoke and outer leg laminations substantially aligned and the ends of each of the laminations in each layer overlapping the ends of the corresponding laminations in the adjacent layers.

22. A three phase magnetic core of the core form type comprising, a plurality of layers of laminations formed from a magnetic strip material having a preferred orientation parallel to the sides of said material,

each of said layers including at least two yoke laminations and two outer and one inner leg laminations assembled around two substantially rectangular windows and forming four substantially squared outer corners, the adjoining ends of said laminations being substantially aligned to form diagonal joints, the ends of said inner leg lamination being cut in substantially a V-shape, said yoke laminations having recesses cut therein which will receive the ends of said inner leg lamination, the ends of each of said yoke and outer leg laminations being cut diagonally with respect to the sides of said strip material and at least one end of each of said yoke and outer leg laminations including a portion cut substantially normal to the sides of said strip material to form a substantially rectangular corner on each lamination, said layers of laminations being divided into groups, each of said groups including a plurality of layers, the normal cuts of the ends of said yoke and outer leg laminations being made in stepped relation in successive layers forming a stepped pattern on one side of each outer corner of said magnetic core, said stepped pattern being formed by stepping at least three successive layers of said laminations in the same direction, the layers of each group being stacked with the rectangular corners of said laminations substantially aligned and the ends of the laminations in each layer overlapping the ends of the laminations in the adjacent layers, the extent of the overlapping of the ends of each of said laminations by the ends of the laminations in the adjacent layers being at least six times the thickness of each lamination.

References Cited in the file of this patent UNITED STATES PATENTS 852,712 Frank May 7, 1907 2,300,964 Putman Nov. 3, 1942 2,407,625 Brand Sept. 17, 1946 2,628,273 Somerville Feb. 10, 1953 2,898,565 Fox et a1. Aug. 4, 1959 FOREIGN PATENTS 592,020 Great Britain Sept. 4, 1947 

1. IN A MAGNETIC CORE, THE COMBINATION COMPRISING A PLURALITY OF LAYERS OF LAMINATIONS FORMED FROM A MAGNETIC STRIP MATERIAL HAVING A PREFERRED ORIENTATION LENGTHWISE OF SAID STRIP MATERIAL, EACH OF SAID LAYERS INCLUDING AT LEAST FOUR LAMINATIONS ASSEMBLED AROUND A SUBSTANTIALLY RECTANGULAR WINDOW AND FORMING FOUR OUTER CORNERS, THE ADJOINING ENDS OF SAID LAMINATIONS IN EACH OF SAID LAYERS BEING SUBSTANTIALLY ALIGNED TO FORM DIAGONAL JOINTS, SAID LAMINATIONS HAVING ENDS SHEARED DIAGONALLY WITH RESPECT TO THE LONGITUDINAL DIMENSION OF SAID STRIP MATERIAL WITH AT LEAST ONE END OF TWO OF SAID LAMINATIONS ALSO INCLUDING A PORTION CLIPPED SUBSTANTIALLY PERPENDICULAR TO THE LONGITUDINAL DIMENSION OF SAID STRIP MATERIAL TO FORM A 